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Keywords:

  • organic matter;
  • gut content;
  • aquatic insects;
  • stable isotope analysis;
  • alpine streams

Abstract

Alpine stream systems are known to be affected by the prevailing water sources (glacial, non-glacial), regional climate and the vegetation of the watershed. Especially at higher altitudes, these conditions influence and shape abiotic factors and the biology of stream reaches, there usually resulting in harsh environmental settings for the biota. Little is known about nutrients, food availability and food utilization in these systems. We investigated the physico-chemical conditions, food resources (DOM, CPOM, FPOM, seston, Aufwuchs) and the bottom fauna in nine reaches of different stream types (glacial, non-glacial systems) above and below the treeline in two seasons. Gut content and stable isotope (δ 15N, δ 13C) analysis were used to estimate food consumption and assimilation for dominant species. Although most of the taxa were detritivores, some species showed a preference for specific food items. Both, the principal dietary component as well as stable isotope analyses confirmed the placement of taxa into functional feeding guilds. In addition the results of stable isotope analysis suggested opportunistic feeding of several species. Autochthony appeared to play an important role even in glacial streams, where long snow cover, frequent flooding and high turbidity limit Aufwuchs development for most months of the year.